City dwellers in the distant future could be squeezed out of the United States’ biggest coastal cities by sea level rise, if new research is right. Miami, Boston and Sacramento are just some of the cities that could be locked in to serious levels of flooding by 2100 if high emissions scenarios are realised, it says.

That’s not to say these cities would be entirely underwater by 2100 – a mistake made but quickly corrected bythe Guardian. But the emissions released over this century could mean these cities are unable to escape flooding from sea level rise at some point over the coming centuries or millennia. Here are the finer details of the study.

Lock in

The idea of long term sea level rise caught media attention earlier this month when researchin the journal Proceedings of the National Academy of Sciences (PNAS) estimated that for each degree Celsius of global warming, sea levels would rise by2.3 metres.

This long term picture is important because sea levels respond slowly to temperature rise. This means that even if greenhouse gas emissions are cut and temperatures level out, sea level rise will continue for some time.

Now, a new comment articleby Benjamin Strauss in the journal PNAS takes the idea of long term sea level rise one step further. By looking at the amount of carbon humans have emitted since 1850, plus the amount we might emit by 2100, Strauss estimates the long term effect of this century’s emissions.

By 2050, we’d be locked into 2.1 m of long term sea level rise under a low emissions scenario, or 3.1 m under much higher emissions, according to his modelling.

High tide

By 2100,Strauss estimates, the level of carbon emissions in the atmosphere will have committed Earth to enough long term sea level rise to threaten many of the United States coastal cities.

The scariest scenario occurs if emissions continue to rise unabated out to 2100. At high tide, the locked-in sea level rise would flood land where 50 per cent of the populations of Miami, Boston, Virginia Beach and Sacramento currently live.

However, the research finds that if emissions were to peak soon and fall for the rest of this century, the long term sea level lock-in would be much less. Of the seven large cities the study looks at, only Miami would be severely affected – with residential areas housing 25 per cent of today’s population flooded.

Even if floods affect less than 25 percent of cities’ residential areas, the effect could still be damaging though. Where important infrastructure like power stations and hospitals is very close to the shore lines, limited flooding could have cause significant disruption

Major threat

There are of course caveats with studies like this. People in cities will probably adapt where possible – building coastal defences and migrating inland, for example – so the risk might not be so great in the future.

There could also be some regional difference in sea level rise, so some cities may end up faring worse than others. There are still questions as to whether Miami will end upunderwater, for example.

But the research carries a strong message. Today’s emissions represent a real threat to people living in coastal cities hundreds or thousands of years from now. The decisions governments make about emissions this century may not change sea levels much by 2100, but they will affect climate for a long time to come.